Very nicely done! Even when I figured I knew the story, I was interested in the guy's progression enough to keep me playing. That's a fine job in and of itself.
On that note, DAMN, I did NOT see that plot twist coming. Yeesh. Absolutely morbid. Love it.
The music is nice - it more kinda falls into the background and sets the mood for the game. Makes a wonderful atmosphere, it really does.
The checkpoints were creepy! You've got that atmosphere going!
The gameplay could've been a little different, and the gameplay would've been better but the story really wouldn't have been. Yes, it did admittedly get annoying waiting for each platform, then having to move with it, and often falling off when it was obscured in darkness. But then again, the darkness is pretty symbolic, I think - the game's named "Dark" for a reason. We are actively exploring the darkness in this guy's past, his heart, and his mind. It makes sense that the dark would give him difficulties - everything's coming from dark places here. Ease of gameplay versus story, and story is the support beam of the entire game, so I think you made the right choice with what you did.
I think that covers it... Great idea, great execution. Pun totally intended. You've got yourself a new subscriber, my friend. :3